This invention relates to iron cores for rotary electric machines suitable for use as stator iron cores of AC generators for vehicles, for example, and more particularly it is concerned with what is generally referred to as a wound iron core formed by spirally winding a strip of iron core blank and joining its convolutions together by electric resistance welding. More specifically, the invention relates to a wound iron core and a method of producing same which is formed thereon with improved projections and recesses that enable an iron core blank to be spirally wound and its convolutions to be superposed one above another and welded together with accuracy and precision and in good condition.
A wound iron core is known which is produced by winding a strip of iron core blank formed with a plurality of teeth into a spiral form while subjecting same to plastic deformation and by joining its convolutions together by welding. It is widely known that the use of wound iron cores reduces the amount of sheet steel for the production of iron cores as compared with the use of iron cores of the ordinary type which are each produced by superposing one over another a plurality of annular iron core blanks produced by blanking directly from sheet steel. However, it is also known that difficulties are encountered in positively and precisely winding an iron core blank of strip form in a spiral form and accurately superposing the convolutions one above another in such a manner that the teeth of the adjacent convolutions coincide with one another. Thus it is necessary to satisfactorily solve this problem to put a wound iron core to practical use.
As a method for solving this problem, proposals have been made to utilize the teeth of an iron core blank for winding the blank and positioning the convolutions when they are superposed one above another. It has also been proposed to provide an iron core blank with a plurality of projections extending radially outwardly and spaced apart from one another a suitable spacing interval, such projections being disposed on an edge portion (outer edge portion) of the iron core blank opposite the teeth thereof so that the projections can be used for winding the blank and superposing the convolutions one above another. Some disadvantages are associated with these methods of the prior art. In the former, each of the teeth of an iron core blank might be deformed by a force exerted thereon when the blank is spirally wound. In the latter, the projections would increase the width of the iron core blank, causing the material to be wasted. With these disadvantages, the methods that have hitherto been known for solving the problem are not considered satisfactory, and it has been earnestly desired that some other effective method be developed for obviating the problem.